The invention relates to a process for the preparation of polyols having 3 or 4 hydroxyl groups, from an aldehyde and formaldehyde in the presence of water, followed by hydrogenation of the aldolisation product in the presence of a hydrogenation catalyst at an elevated temperature.
Polyols and especially 1,1,1-trimethylolpropane (TMP) are important starting materials and intermediates in the production of synthetic resins, such as polyester resins and the like. They may also be used in the manufacture of plasticizers, synthetic lubricants, surfactants etc. Polyols like 1,1,1-trimethylolpropane are prepared by allowing formaldehyde and another aldehyde to react in the presence of a strongly alkaline catalyst, such as sodium hydroxide, potassium hydroxide or calcium hydroxide to form a desired alcohol. However, large amounts of formate salts are formed as by-products thus making the process not very attractive for commercial purposes. In another, alternative process the aldolisation reaction of formaldehyde and another aldehyde is carried out in the presence of an amine catalyst, such as triethylamine, followed by hydrogenation. The aldolisation reaction may also be performed with an anion exchange resin acting as a catalyst.
A method for the manufacture of polyalcohols is presented in DE 19542036, wherein an alkanal or ketone is allowed to react with formaldehyde in an aqueous solution in the presence of an amine, then water, excess of amine, excess of formaldehyde and methanol formed from Cannizzarro-reaction with formaldehyde are separated. The remaining reaction mixture is heated and polyalcohol formate is formed. The obtained polyalcohol formate is subjected to trans-esterification with an alcohol in order to obtain the desired polyalcohol, which is isolated from the reaction mixture.
In U.S. Pat. No. 5,144,088 is disclosed a process for the manufacture of a polyol, and especially neopentyl glycol wherein isobutyraldehyde is reacted with paraformaldehyde in the presence of a tertiary amine, preferably triethylamine and of one or more oxides of elements of groups IB, IVA, IVB, VA, VB, VIB and VII of the periodic table and then hydrogenating the obtained monomeric and dimeric hydroxypivaldehyde.
In U.S. Pat. No. 5,146,012 is described a method of making neopentyl glycol by reacting isobutyraldehyde with paraformaldehyde to obtain a reaction product comprising hydroxypivaldehyde, forming a mixture of the reaction product with about 40-90% of an alcohol, preferably methanol and then contacting the mixture with hydrogen in the presence of a hydrogenation catalysts.
A process for the manufacture of polyols is disclosed in FI 965268 wherein an aldolisation reaction is performed with formaldehyde and another aldehyde comprising at least 2 carbon atoms, in the presence of a weakly basic anion exchange resin, followed by hydrogenation which is performed in the presence of a solvent and a hydrogenation catalyst.
A process is disclosed in FI 974638 for the preparation of neopentyl glycol by hydrogenation of hydroxypivaldehyde in the presence of hydrogen and a hydrogenation catalyst containing nickel, at a temperature below 100xc2x0 C. in a liquid phase comprising a solvent in an amount of 1-70 wt %, preferably an aliphatic alcohol or ether or a mixture thereof and water in an amount of less than 15 wt %.
A method is disclosed in JP 10287606 for the purification of dimethylol alkanal. Unreacted formaldehyde is separated from a reaction product containing dimethylol alkanal, obtained by carrying out a condensation reaction of an aliphatic aldehyde with formaldehyde in the presence of a hydroxide, a carbonate or a bicarbonate of an alkali metal or an alkaline earth metal, or other basic catalyst, such as an anion exchange resin and water. Water is added to the reaction product solution so that the water amount is about 4 times by weight, based on the formaldehyde content in the reaction product solution, then the mixture is fed to a thin-film type vaporizer to concentrate the solution and the thus generated formaldehyde vapour and steam are distilled away from one end of the thin-film type vaporizer to purify the dimethylol alkanal.
It has been observed that several problems are related to the methods according to the state of the art. For example, in the first step of the manufacturing process of 1,1,1-trimethylolpropane (TMP), the aldolisation step of the aldehydes, undesired side reactions may occur. When the starting material, such as n-butanal, reacts with formaldehyde, 2-ethyl-3-hydroxypropanal is formed but also as a result of dehydration 2-ethylpropenal (ethyl acrolein) is obtained. 2-Ethyl-3-hydroxypropanal further reacts with formaldehyde to yield the desired intermediate 2-ethyl-3-hydroxy-2-(hydroxymethyl)propanal (TMPA). Because of the side reactions, the yield of the aldol in the aldolisation step and further the yield and purity of the final product are lower. The aldol product 2-ethyl-3-hydroxy-2-(hydroxymethyl)propanal contains varying amounts of unreacted formaldehyde which is a catalyst inhibitor affecting the subsequent catalytic hydrogenation step. To compensate the inhibiting effect of formaldehyde on the hydrogenation reaction, large amounts of the hydrogenation catalyst must be used thus increasing the reactor size and investment costs. Usually, the number of phases of a component depends on the temperature and concentration. If formaldehyde concentration increases, especially at low temperatures below 50xc2x0 C., solid paraformaldehyde is formed, which can cause severe blocking problems in the process. Based on the above it can be seen that there clearly exists a need for an improved process for the manufacture of polyols with improved yields, purity, conversion and selectivity.
The invention relates to a process for the preparation of polyols by aldolisation of an aldehyde with formaldehyde over an anion exhange resin catalyst, followed by hydrogenation of the aldol product over a supported metal catalyst.
Characteristic features of the process for the preparation of polyols are stated in the claims.